Generally, an integrated circuit chip includes a logic function circuit and a power supply circuit. The logic function circuit is implemented by a complementary metal-oxide-semiconductor (CMOS) transistor. The power supply circuit is implemented by a high voltage metal-oxide-semiconductor field-effect transistor. However, the conventional isolated high voltage N-channel metal-oxide-semiconductor field-effect transistor (also referred as an isolated HV-NMOS) has some drawbacks. For example, due to the structural defect, a current leakage problem possibly occurs, and thus the charge pump circuit usually has a failure. Therefore, there is a need of providing an improved method to solve these drawbacks.